Animal tissues



Patented Aug. 12, 1952 OFFICE PROCESS FOR PRESERVING PLANT AND ANIMAL TISSUES George R. Fessenden, Baltimore, Md.

No Drawing. Application January 7, 1949,

Serial No. 69,840

7 Claims. 1

This is a continuation-in-part of my co-pending application for patent, Serial No. 736,105, filed March 20, 1947, now Patent No. 2,567,929, and relates to a method for preserving biological material, both plant and animal, in a manner that provides for enduring retention of the natural appearance, including color and shape, in material which has generally unstable or impermanent appearance characteristics.

Material so preserved is of. particular value as museum specimens and is widely useful for educational purposes in the natural sciences and elsewhere. Furthermore, it has unique value for decorative and ornamental use, for product demonstration, display use, and for various other self evident purposes.

The practices heretofore commonly employed for preserving biological material, such as flowers and other plant parts, and zoological specimens, for the purposes enumerated above have given no special attention to the paramount consideration of insuring permanence in the natural appearance of the preserved material in a manner true to the original living specimens, particularly where the color is unstable during processing or subsequently thereto. That is to say, prior prac-' tices in preparing and preserving most biological material yield products that only partially fulfill the desired requirements, in that the natural color is not rendered permanent, or it is undesirably altered, or it is replaced by artificial coloring matter, and the preserved material is not adequately protected against deterioration with respect to its appearance.

Accordingly, with a view of avoiding the objections above recited, and solving the various problems incident to the previous shortcomings of the art, a primary object of the present invention is to employ new procedures for preserving biological'material, which is commonly subject to change in appearance, in a manner to retain enduringly its natural appearance, including color and shape, and for providing such preserved material with durable and effective protection against deterioration and damage without undesirably altering its natural appearance in so doing.

The foregoing primary object, namely, to prepare biological material so that its natural appearance, including color and shape, is enduringly preserved, is carried out in accordance with this invention by stabilizing the color by chemical treatment and fixing the shape'by dehydration, impregnating and/r coating the material thus prepared with a shape-reinforcing substance which is impervious to and/or unafiected by a subsequently applied enveloping medium and which prevents alteration of the natural appearance of the materialby such medium, and then protecting the impregnated and/or coated material by surrounding it with a relatively thick mass of transparent, moisture-excluding, durable plastic.

In the preparation of this preserved material, it has been found that biological objects vary t v such an extent that difierent procedures are" necessary to preparing the diverse classes of material so that the natural'appearance, including color and shape, is not altered through processing and is enduringly retained thereafter under conditions of ordinary use.

Therefore, biological material may, from the point of view of processing, be classified, for convenience, with respect to retention of appearance characteristics, as follows:

Class A comprises material in which the color is naturally unstable, and is irreversibly altered by air-drying. This class has been found to include such material as the flowers and leaves of most orchid, gardenia,-indianpipe, and mallow species; the flowers of many poppy, verbena, trumpetcreeper, and Camellia species; the leaves of many mint, spurge cactus, Pelargonium and Cinchona species; most of the fleshy fruits and the fleshy fungi; and zoological organisms in general with the exception of the groups noted in the remaining classes.

Class B comprises material in which the color is naturally unstable, but is not irreversibly altered by air-drying. This class has been found to include generally the diverse forms f plant material not specified in the other classes; and such zoological material as the green-pigmented locust, cricket and Mantis species.

Class C comprises material in which the color does not require stabilization but the appearance is subject to alteration by the enveloping medium. This class has been found to include lichens, decayed wood, woody fungi, bark, feathers, and lepidopterous insects.

Class D comprises material in'which color and shape are naturally stable and the appearance is not objectionably affected by the enveloping medium. This class comprises matured everlasting flowers such as the everlasting species of the amaranth and the composite families, matured grains and other grasses, cones, nuts and various dried fruits, and most woody or hardened parts of plants not noted in the foregoing class; and it further includes the durably pigmented insects which have rigid integuments, and such other zoological material as teeth, bones, carapaces, shells, horns and claws.

The present invention is primarily concerned with Classes A, B, and C wherein the color of the material must be considered. with respect to its stability during processing and subsequently thereto. Material in Class D may be utilized as desired in its natural state, or it may be dehydrated and enveloped in any well known manner without other preparation.

According to the present invention, the processing of biological material so as to preserve enduringly its natural appearance, consists generally of three stages, namely, Stage I-Stabilizing Natural Color and Dehydrating; Stage II-- Impregnating; Stage III-Enveloping. Stage I is carried out by procedures employed selectively in accordance with the characteristics of the material being processed, are carriedout. by. procedures employed, selectively in, accordance both with. thenature. of; the material being processed. and. with. the use. to. which the finishedproductisto be. put.

Each of the-foregoing. stages comprises .a number' of new and improved steps, andprocedures which are employed selectively in accordance with the requirements of the classes of, material to be processed, and. which may beemployed in the sequence givenor otherwise, and. separately or in combination .with eachother.

Theterminology hereinafter. usd in describing the several actions, substances andv materials is to be construed in the lightof. the following definitions; material is intendedto mean biological material; solution isintended to include dispersions as. well as true solutions; dissolve is intended to include the dispersion of substances in liquids aswell astheforming of, true solutions; the term water-dissolving as applied toanother liquid is intended to mean that the liquid has-the property ofbeing able to hold in solution withinitself an amount of. water equal to at leastoi:the total weight of the solution; the noun plastic is-intended to apply'to resins andother water-resistant substances which are in a polymeric state or capable of being polymerized, and are plastic in. that they are capablev of being cast, molded, formed, or otherwise shaped by heat and/or pressure; dehydration is intended to mean removal of the water content to an extent sufficient toarrest chemical and physical changes w-hichtendto occur. when free moisture is present; impregnation is intended to mean saturating apermeable materialwitha substance, leaving a minimum. thereof on the surface; the term enveloping is intended to mean selectively-,. coating, encasing, laminating or embedding; the term conditioning agent. applies to substances employed for the purpose of modifying strength and rigidity characteristics and/or. of. preventing physical change in appearance factorsduring processing.

The stages generally describedabovewill now be set forth in greater detail.

STAGE I. STABYIILiIZINC-r NATURAL COLOR AND DEHYDRATING Inthe first stage of preparing biological material. in which the. natural appearance, including, color and shape, are enduringly retained, the material, which may either be fresh or previously dried, is subjected to a chemical preserving treatment which maintains, or rte-establishes, the original colorand stabilizes it against subsequent and, Stages II andIlI.v

, fromv active reducing change. This chemical treatment consists in subjecting the material to a treating solution comprising a water-dissolving volatile organic liquid containing an oxidation inhibitor and a preserving substance which controls the hydrogen ion concentration and stabilizes the color and composition of the material- With these substances may be further employed selectivel a limited amount of water, a surface-active substance and a conditioning agent. The specific constituents of the solution and the amounts in which they are employed are dependent upon the nature of the particular material to be treated, their selectionbeing determined experimentally in accordance therewith from the classes of substances liereinaiter described, their amounts being confined within the limiting ranges specified.

The preservation treatment is followed by dehydration to remove such free water as may have remained in the preserved material, this. dehydrationgbeing carried-out in a manner that provisionally maintains the stabilized color and shape, andlprepares the preserved material for impregnating and/ or enveloping procedures subsequently tobecarried out in Stages II and/ or III.

Stage 1; Procedure, 1

Biological material coming Within Class A, i. e., material in which the color is naturally unstable and isirreversibly altered by air-drying, is immersed While still'in a fresh" condition in a treating solution which consists of suitable constituents hereinaiter'described dissolved or dispersed in a water dissolvmg' volatile liquid which is practically free from detrimental effect upon the material when employed in combination with the treating agents specified; Theliquids employed for this purpose may be selected. from a group which includes monohydrio alcohols such as the butyl and the. amyl' alcohols; ketones, such as acetone, diacetone. and methyl-ethyl ketone; esters such as ethyl acetate, ethyl lactate, and triethylphosphate; and ethers such as dioxane andethylene glycol monomethyleether; and these liquidsmay be used separately or in combination with each other, or with other liquids which are misciblewiththem but. are not water-dissolving, such as turpentine and the aliphatic and the aromatic hydrocarbons. Both the treating agentsand the volatile liquid vehicle in which they are incorporated are employed selectively in accordance, with, the individual requirements of the material, and the treating agents generally comprise:

(a) Oxidation inhibitorswhich are employed selectively with, respect to. the characteristics of the coloring matter inthe material to be treated, and arechosenso as to. prevent oxidative alterationinits appearance without causing bleaching or other appearancechanges that might result action exerted upon the natural color matter. For material not generally altered. in appearance by reduction, an oxidation inhibitor is used which is selected from the group of salts containing a. sulfite radical such as sodium sulfite, or containing a nitrite radical such as sodium nitrite, or containing a phosphite radical such. as potassium phosphite; or from a group of quinones suchas hydroquinone; or from a group of. aldehydes such as formaldehyde; or from agroup of, oxidizableorganic acids such as ascorbic acid; and. these substances may be employed separately, or in combination with each other or with generally non-reducing anti-0xidants; For material containing anthocyanin Digments or other coloring matter which is altered in appearance by reduction, an oxidation inhibitor selected from the group of generally nonreducing anti-oxidant substances containing a sulfhydryl or an S=C= radical, such as thiourea, is employed in place of a reducing type of oxidation inhibitor. Oxidation inhibitors are employed selectively in amounts ranging from 0.1% to 10% of the total weight of the solution, the optimum being determined in accordance with the requirements of the material undergoing preservation.

(b) The substance used for preservation of the tissue and stabilization of the natural color is an ionizing compound selected from the group ineluding, but not limited to, non-oxidizing acids such as boric, phosphoric, arsenic, citric, tartaric, acetic, and lactic, and the alkali metal and alkaline earth metal, salts of such acids. These compounds are selectively employed singly or in combination with each other or with other similarly constituted compounds, and they are generally used in such proportions as to maintain the pH of the mixture at the value required for retention of the true natural color in the material undergoing preservation. The amounts of these substances or mixtures thereof incorporated in the treating solution range from 0.5% to 10% of the total weight of the solution.

Surface-active substances may be employed in the treating solution in accordance with the requirements of the material being preserved in order to maintain a suitable dispersion of such treating substances as may not be soluble in the liquid medium employed for the treating solution, and/or to obtain a more uniform and rapid response of the material to the various treating substances incorporated in the solution. The substances generally used for this purpose are preferably, but not essentially, of the non-ionizing type and are generally selected from a group of partial esters of polyhydric alcohols with long chain fatty acids, e. g., sorbitan monolaurate, and their polyoxyalkylene esters; and the amounts employed range from 0.1% to 2% of the total weight of the solution.

(d) Conditioning agents may be employed for the purpose of maintaining the opacity of the material and of modifying its rigidity or its flexibility, and of counteracting appearance changes that might otherwise be produced in it by dehydration or by extraction of soluble constituents during treatment. The substances thus used are employed selectively in accordance with the requirements of the material and include liquid organic silicon compounds; high boiling oily liquids such as dibutyl phthalate, butyl phthalyl, butyl glycolate, tributyl citrate, methyl abietate, tributyl phosphate, natural fixed oils such as c0ttonseed, palm, castor, teaseed, and neatsfoot oil,

and drying oils such as linseed, tung, soya and dehydrated castor oil; such waxy substances as beeswax, Chinese wax, Japan wax, carnauba wax, montan wax, ceresin, spermacetti, polyethylene glycol, and paraffin; plastic or resinous substances such as polyvinyl acetate and the polybutyl methacrylates, hydrogenated rosin, hydroabietyl alcohol, hydroabietyl borate, hydroabietyl maleate, hydroabietyl stearate, ester gum, glyceryl phthalate, sucrose octa-acetate; and natural gums and resins such as Canada balsam, shellac, mastic, sandarach, copal. elemi, dammar, rosin. and Venice turpentine. The amount of a conditioning agent employed ranges from 1% to of the total weight of the solution.

(6) A limited amount of water is generally employed in the treating solution in order to increase the ionization of thewate'r-soluble constituents, and to prevent shrinkage or other shape change in the material which might result from too rapid dehydration while undergoing preservation. The amount of water maintained in the solution for these purposes rangesfrom 1% to 20% of the total weight of the solution and may be regulated through the use of substances which absorb Water selectively with respect to the other constituents and which have no adverse efiect upon the material being preserved. For this purpose such substances as cellulose fiber and Watersoluble cellulose derivatives, agar, gelatin, algin, polyvinyl alcohol, silica gel, anhydrous calcium sulfate, and calcium chloride may be employed selectively and the amount used depends upon the extent to which thewater content may require regulation, generally. ranging from 5% to 25% of the total weight of the dehydrating liquid. i The material while undergoing treatment is kept submerged in the treating solution for a period ranging from 1 to 24 hours, according to its permeability and the temperature at which it is maintained. During immersion, it is:preferable to keep the temperature of the solution betweenithe limits of 5 and +5 C., butaacceptable results are obtainable at room temperature or at moderately elevated temperatures. 1 Completion ofthe preserving action of the solution is :generally indicated by the material assuming a'more or less uniform translucentappearance asa result of be-'- ing fully permeated by the solution;

When the material has become adequately preserved, it is subjected to dehydration in order to remove the water remaining inxit as'a result of the color-stabilizing treatment. -xDehydration is carried out according tov well known procedure, either by transferrin the preserved material from the moisture-containing treating solution into a moisture-free water-dissolving volatile liquid, which may be the same as, 'or'difi'erent from, the volatile vehicle employed in the treating solution, and this transfer'may be made directly, or through one or several intermediate baths, each of which contains less moisture than the preceding, the final one being: practically anhydrous; or by air-drying the preserved material at full atmospheric pressure or at a reduced pressure under conditions where a relative humidity lower than 20% is maintained by employment of desiccant, and/or elevated temperatures within the range tolerated by the appearance factors of the material, and generally not in excess of 75 C. or by removal of moisture by means of low temperature condensing elements. fiubsequent to dehydration, and pending {impregnation and enveloprnent by the procedures described; for Stages II and III, the material is kept in a practically moisture-free state, either in an anhydrous liquid or in an airtight and preferablydesiccated container.

Stage I.-Procedur e 2 Biological material coming within Class B, i. e., material in which the color is naturally unstable, but is not irreversibly altered by air-drying, is preferably subjected to preliminary air-drying in such a manner as to maintain the natural color and shape provisionally, either without change, or in a condition that permits of re-establishment by subsequent treatment. This preliminary airdrying is carried out by well known procedures which consist in subjecting the fresh material to ing mediums are used selectively air, the relative humidity of whichis generally maintained'below 20%, either at fullatmospheric pressure or at reduced pressure, by means of desiccants such as anhydrouscalcium sulfate, calcium chloride, silica gel, concentrated sulfuric acid, or phosphoric anhydride, and/or by means of elevated temperatures, not exceeding 75 6., within the range of tolerance of the appearance factors in the materiahand/ or by means of refrigerated condensing elements which remove the moisture in the form of frost or ice, or by freezing the material and removing the moisture in it by sublimation under reduced atmospheric pressure.

Material in Class B which is not of suiilciently rigid structure toundergo air-drying without deformation, is supported during dehydration according to well known practice by being surrounded with a non-caking moisture-permeable medium such as sandpsilica gel,-talc, starch, agar, corn meal, glass beads, granular polymethyl methacrylat polyvinyl acetate, polystyrene, cellulosic derivatives, flowers of sulfur, boric acid, borax, tmagnesium 'trate, anyhydrous calcium sulfate, or sodium fiuosilicate; and these supportandmay be em: ployed separately or in combination with each other or with other substances. Dehydration of material packed in such a supporting medium is generally carried out under conditions described in the preceding paragraph which maintain a lower external .relative' humidity than exists within the supporting medium, and is allowed to proceed for a period of time generally ranging from 1 hour to 3 days according to the nature of the material and the conditions under which dehydration is carried-out.

When dehydration has been carried to a degree where practically all free moisture has been removed, the supporting medium is removed from the surface of the dehydrated material, preferably with a feather ora jet of air.

Material which has thus been air-dried is subsequently processed to render its appearance enduringly stable in the manner described in Stage I, Procedure 1, by immersing it while in the dry state in'a color-stabilizing preserving solution and finally dehydrating it to remove moisture that may have re-entered it during treatment; it is then kept in a practically moisture-free state pending impregnating and/ or envelopment,

Stage I .-Procedure 3 Biological material comingwithin Class C, i. e., material in which the color requires no stabilization but the appearance is subject to alteration by the enveloping medium, color-stabilization treatment is omitted and preparation for envelopment is confined to dehydration. Dehydration of material in this class may be carried out in the manner described in Stage I, Procedure 2, or it may be accomplished in accordance with well known practice by immersion in water-dissolving volatile organic liquids such as ethyl alcohol, acetone or dioxane. Subsequent to dehydration the material is kept in a practically moisture-free state pending impregnation and/ or envelopment.

STAGE II.- -IMPREGNATION Biological material coming within Classes A, B, and C, which has been preserved and/or dehydrated by the procedures described in Stage I may be impregnated either with a moisture-resistant shape-reinforcing substance which protects it'from deterioration and provides it with a substance which is impervious to and/or unaffected by a subsequently applied enveloping medium and which prevents alteration of its natural appearance by such medium when applied.

Stdge II .--Proccdure 1 Preserved and dehydrated material which has been prepared by the procedures in Stage I, selectively employed, is immersed in a bath of moisture-resistant shape-reinforcing substance, to which a subsequently applied protective coating will adhere securely, dissolved in a suitable moisture-free volatile organic liquid vehicle such as toluene, and which is preferably, but not neces sarily, maintained at an elevated temperature not in excess of 0.; and the material is kept submerged therein for a period of time ranging from less than 1 minute to 4 hours, dependent upon the nature of the material and the tem perature employed, until it is practically completely permeated with the impregnating substance; and this may be done at atmospheric pressure, or under increased pressure or under decreased pressure. The impregnated material is then removed from the bath, and the volatile solvent vehicle which has served as the vehicle for the impregnating substance is allowed to evaporate, preferably in freely moving air which has a relative humidity below 30%, which condition may be maintained by elevation of temperature not in excess of 100 C., and/or by means of commonly employed desiccants.

The impregnating substance employed for this purpose consists of a suitably moisture-resistant and adhesive solid or solidifiable substance selected from a group of waxy substances such as carnauba wax, montan wax, ceresin, microcrystalline paraffin having a melting point of 70 C. or higher, highly chlorinated hydrocarbons, and polyethylene glycol; or drying oils and semi-drying oils such as linseed, tung, soya and dehydrated castor oil, or plastic and resinous substances such as vinyl acetate-chloride copolymer, polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, methyl, ethyl and butyl methacrylate polymers, polyethyl acrylate, polystyrene, hydrogenated rosin, hydroabietyl alcohol, ester gum, glyceryl phthalate, sucrose octet-acetate, aryl sulfonamide-formaldehyde resins, courmarone-indene polymers, polymerized terpene resins, diene polymers and natural rubber, and organic silicon resinous compounds; or natural gums and resins such as rosin, Canada balsam, shellac, mastic, sandarach, copal, elemi and dammar. Substances selecterl from these groups may be used separately or in combination with each other or with a plasticizer such as dibutyl phthalate, butyl phthalyl butyl glycolate, or tricresyl phosphate, which may desirably modify their toughness and flexibility characteristics; and the amount of the impregnating substance dissolved in the volatile liquid vehicle generally ranges from 5% to 40% of the total weight of the solution, depending upon the substance and the solvent vehicle employed.

Material thus impregnated may be utilized for practical purposes without further processing, or it may be provided with additional protection against deterioration and enhanced in usefulness and attractiveness by being enveloped in a coating or armor, or in a case as set forth in Stage III, Procedures 1 and 2, respectively,

Stage I I .-Procedure 2 Preserved and dehydrated material which has been prepared by the procedures described in Stage I, selectively employed, is immersed in a bathof polymerizable moisture-resistant plastic which is in a monomeric or a partially polymerized liquid state and contains from 0.01 to 0.5% of a polymerization catalyst, such as benzoyl peroxide, and the material is'kept submerged therein until practically complete permeation has occurred. This is done preferably under reduced atmospheric pressureand at room temperature, and the state of practically complete permeation is generally indicated by the cessation of air bubbles rising from the material. The permeat ed material is then subjected, in accordance with well known practice, to moderate heat and/or light until the impregnating plastic within it is polymerized to its 'solidstate, which may require from 30 minutes to days, depending upon the nature of the impregnating substance, the kind and amount of catalyst employed and the polymerization-promotingconditions to which it is subjected. The impregnating substance used for this purpose may be selected from the group of polymerizable plastics which includes, but is not limited to, the methyl, ethyl and butyl methacrylates, ethyl acrylate, vinyl acetate, allyl starch, diethylene glycol bis (allylcarbonate), styrene, alkyd-styrene compositions, and phenol-aldehyde, urea-aldehyde and melamine-aldehyde partial condensates; and substances selected from this group may be used singly or in compatible mixtures with each other or with such commonly employed plasticizing agents as dibutyl phthalate, butyl phthalyl butyl glycolate, and tricresyl phosphate. Material thus impregnated may be utilized for practical purposes without further processing, or it may be provided with additional protection against deterioration by being enveloped in accordance with the proced ures set forth in Stage III, selectively employed to obtain the type of finished product desired.

Stage II .Proccdure 3 Preserved material which is subject to alteration of natural appearance as a result of contact with a plastic enveloping medium subsequently to be applied, and which is also altered in appearance by contact with a lipophilic substance, may be protected from such appearance alteration by being impregnated with a hydrophilic substance which is unafiected by and impervious tov the subsequently applied enveloping medium and which possesses suitable shape-reinforcing properties.

Such protective impregnation is accomplished by immersing the prepared material in an aqueous solution of solidifiable water-soluble gummy substances, such as agar, algin, gelatin, gum acacia, pectin, starch, polyvinyl alcohol, polyethylene glycol, sorbitol borate, sorbitol citrate, sorbitol boriphosphate, glycerol borate, sucrose and hexose sugars, or a solution in a volatile organic liquid such as microcrystalline parafiins, highly chlorinated hydrocarbons,.such as parafiin, naphthalene, and diphenyl; and allowing the material to remain submerged at room temperature or at moderately elevated temperature, and preferably under reduced atmospheric pressure, until practically complete permeation has been obtained. The permeated material is then removed and the moisture in itremoved by dehydration in the manner described in Stage I, Procedure 1, whereupon it becomes effectively resistant to the appearance-changing action of a subsequently applied plastic enveloping medium.

The impregnating substances selected from the .10 above group may be used separately or in compatible combinations with each other or with other substances havingsimilar properties; and the amount of the impregnating substance dissolved in the water ranges generally from 5% to of the, total weight of the solution.

STAGE'III.ENVELQPMENT- In the case of biological material in which the true natural color is to be enduringly retained, its successful envelopment in a protective medium has heretofore been restricted to Class D, that is, to material in which both color and shape are naturally stable; whereas, material which is unstable in its appearance has not heretofore been susceptible of envelopment in a manner to retain enduringly its true natural appearance characteristics.

On the other hand, by following the teaching of the present invention, it is possible to envelop material in Classes A, B and C, having unstable appearance characteristics, in a manner that will Stage III .Proc edure 2 Biological material coming within Class C, i. e.,

aeoaeac material in which the color does not require stabilization, but the appearance is subject to alteration by the enveloping medium, may, afterbeing dehydrated asset forth in Stage I and protectively impregnated by employing selectively Stage II-Procedures 1, 2 or 3, be embedded without alteration of itsnatural appearance by surrounding it with a mass of fluid polymerizable transparent durable plastic-forming substance containing a polymerization catalyst, and then polymerizin the same to a solid state through use of moderate heat and/or light in the manner set forth under Stage Hi -Procedure 1. The plastic-forming substance employed for this pur pose is selected from the group including the methyl and ethyl methacrylates, ethylene glycol bis (allyl-carbonate), styrene, alkyd-styrene compositions, and other polymerizable polyester compositionsyand these are employed in'monomeric or partially polymerized fluid form containing a suitable polymerization catalyst, and subsequently solidified while'surroundingthe material by polymerization efiected by moderate heat and/or light in accordance with well known practice.

EXAMPLES.

Example 1 A blue bachelors-button flower (Centaarea charms) was packed in anhydrous 22-28 mesh silica gel and maintained for 20 hours at a temperature of 45 C. under a partial vacuum of 29 inches. It was then removed and while still in a dry state was immersed in 500 grams of a solution consisting of ethyl acetate containing 1% boric acid (5 grams) 3% sodium borate grams), 0.5% thiourea (2.5 grams), and 0.1% sorbitan monolaurate polyoxyalkylene partial ester. i

It was kept submerged hours at room temperature and then freed of the ethyl acetate remaining in it by being exposed to freely moving air having a relative humidity of y v V V The preserved dehydrated material was then immersed for 2 hours in 500 grams of a solution consisting of toluene containing 20% chlorinated naphthalene (100 grams, and 5% polyethyl methacrylate, and maintained at a temperature of 75 C.

Upon removal of the impregnated material from this solution, the toluene remaining in it was eliminated by evaporationin. freely moving air having a relative humidity of The material was then placed, on a block of polyethyl methacrylate in a Pyrex glass container and was surrounded with moderately viscous fluid ethyl methacrylate partial polymer containing 0.05% benzoyl peroxide. The container was covered with tinfoil to minimize vapor loss, and then subjected to a partial vacuum or 29 inches for a period of 2 hours in order to remove impounded air from the embedding medium.

The impregnated material surrounded by the embedding medium in the covered container was then maintained at a temperature of C. for 2 days, followed by C. for 2 days and C. for 2 days, by which time the ethyl methacrylate had polymerized to a clear solid enveloping block.

This block was tainer, and the material in the removed from the glass conresulting product in this solution for a highly wa'sfound to have retained'its natural appearance, including color and shape, and was resistant to deterioration and damage under natural conditions. l

Example 2 Two light red rose petals were preservedv and dehydrated by the same procedure employed in Example 1 and were then immersed in grams of an aqueous solution containing 40% sodium sorbitol borate (4.0 grams), having a pH of 4.5, and.0'.2% sorbitan monolauratepolyoxyalkylene ester (0.2 gram). The material was kept immersed in this solution for 2 hours at a temperature of 5* C'., and was then transferred to a dehydrating bath of butyl alcohol where it was allowed to remain for 30' minutes.

Upon removal from the dehydrating bath, the alcohol was allowed to evaporate in freely moving air having a relative humidity of 15%, and it was embedded bysurrounding it with fluid ethyl methacrylate partial polymer containing 0.1% benzoyl peroxide, and then polymerizing the same to a solid state by the procedure employed in Example 1. The material in the resulting product was found to have retained its natural appearance, including color and shape, and was resistant to deterioration and damage under natural conditions.

Example 3 A fragment of mold (Penicillium notat'um) was dehydrated in a closed chamber over anhydrous calcium chloride, and was then immersed in 100 grams ofan aqueous solution containing 58% sodium sorbitol borate (50 grams) having a pH value of 6.0, and 10% non-crystallizing sorbitol syrup (10 grams). It was kept, submerged in this solution for 10 days at room temperature, and. was then removed and dried in air having a relative humidity of 10% maintained at a temperature of 50 C.

This impregnated and dehydrated material was embedded by surrounding it with catalyzed fluid methyl methacrylate partial polymer and then polymerizing the same to a solid state by the procedure employed in Example 1. The material in the resulting product was found to have retained its natural appearance, including color and shape, and was resistant to deterioration and damage under normal conditions.

From the foregoing, it is believed that the invention will be readily understood by those skilled in the art. It is also to be understood that the specimens preservedv by the method described and claimed in my co-pending application Serial No. 736,105, filed March. 20, 1947., having athin outer coating applied after impregnation may be embedded, in a polymerizable liquid in accordance with the invention described herein, said thin coating serving, to. protect both the preserved material and the impregnant from any adverse effects of the polymerizable liquid or of any ingredients added thereto, such as catalysts, accelerators, promoters, and so forth, normally used with such embedding substances.

I claim:

1.,A process, for preserving naturally colored plant and animal tissues, comprising, immersing the tissues in a color stabilizing and preserving solution containing essentially a volatile water-dissolving monohydric alcohol and thiourea, said solution being adjusted to a pH corresponding substantially to the pH of the liquid'medium of the tissues in which the natural colorin matter is suspended, removing the tissues from .solution containing 13 the solution and permitting the volatile constituents retained in them to evaporate, whereby the natural colors of the tissues are stabilized and their physical shapes are retained, then impregnating the tissues with a member selected from the group consisting of polyethylene glycol, glycerol borate, sorbitol boriphosphate, sorbitol borate, sorbitol citrate, sucroseand hexose and then applying to said tissues a substantially transparent moisture-resistant resinous coating.

2. A process for preserving naturally colored plant and animal tissues, comprising, immersing the tissues in a color stabilizing and preserving solution containing essentially a volatile waterdissolving monohydric alcohol and thiourea, said solution being adjusted to a pH corresponding substantially to the pH of the liquid medium of the tissues in which the natural coloring matter is suspended, removing the tissues from the solution and permitting the volatile constituents retained in them to evaporate, whereby the natural colors of the tissues are stabilized and their physical shapes are retained, then impregnating the tissues with polyethylene glycol, and then applying to said tissues a substantially transparent moisture-resistant resinous coating.

3. A process for preserving naturally colored plant and animal tissues, comprising, immersing the tissues in a color stabilizing and preserving solution containing essentially a volatile waterdissolving monohydric alcohol and thiourea, said solution being adjusted to a pH corresponding substantially to the pH of the liquid medium of the tissues in which the natural coloring matter is suspended, removing the tissues from the so- I lution and permitting the volatile constituents retained in them to evaporate, whereby the natural colors of the tissues are stabilized and their physical shapes are retained, then impregnating the tissues with sorbitol boriphosphate, and then applying to said tissues a substantially transparent moisture-resistant resinous coating.

4. A process for preserving naturally colored plant and animal tissues, comprising, immersing the tissues solution containing essentially a volatile waterdissolving monohydric alcohol and thiourea, said solution being adjusted to a pH corresponding substantially to the pH of the liquid medium of the tissues in which the natural coloring matter is suspended, removing the tissues from the solution and permitting the volatile constituents retained in them to evaporate, whereby the natural colors of the tissues are stabilized and their physical shapes are retained, then impregnating the tissues with sorbitol borate, and then applying to said tissues a substantially transparent moisture-resistant resinous coating.

5. A process for preserving naturally colored plant and animal tissues, comprising, immersing the tissues in a color stabilizing and preserving essentially a volatile waterdissolving monohydric alcohol and thiourea, said in a color stabilizing and preserving 6. A process for solution being adjusted to a pH dofr'es'poridi'rig substantially to the pH of the liquid medium of the tissues in which the natural coloring matter is suspended, removing the tissues from the solution and permitting the volatile constituents retained in them to evaporate, whereby the natural colors of the tissues are stabilized and their physical shapes are'retained, then impregnating the tissues with sorbitol citrate, and then applying to said tissues a substantially transparent moisture-resistant resinous coating.

preserving naturally colored plant and animal tissues, comprising, immersing the tissues in a color stabilizing and preserving solution containing essentially a volatile waterdissolving monohydric alcohol and thiourea, said solution being adjusted to a pH corresponding substantially to the pH of the liquid medium of the tissues in which the natural coloring matter is suspended, removing the tissues from the solution and permitting the volatile constituents retained in them to evaporate, whereby the natural colors of the tissues are stabilized and their physical shapes are retained, then impregnating the tissues with glycerol borate, and then applying to said tissues a substantially transparent moisture-resistant resinous coating.

7. A process for preserving naturally colored plant and animal tissues, comprising, immersing the tissues in a color stabilizing and preserving solution containing essentially a volatile waterdissolving monohydric alcohol and thiourea, said solution being adjusted to a pH corresponding substantially to the pH of the liquid medium of the tissues in which the natural coloring matter is suspended, removing the tissues from the solution and permitting the volatile constituents retained in them to evaporate, whereby the natural colors of the tissues are stabilized and their physical shapes are retained, then impregnating the tissues with polyethylene glycol, and then enveloping said tissues in alkyd-styrene copoly- GEORGE R.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Preserved in Plastics, Scientific American. vol. 161, No. 4, October 1939, p. 217. 

1. A PROCESS FOR PRESERVING NATURALLY COLORED PLANT AND ANIMAL TISSUES, COMPRISING, IMMERSING THE TISSUES IN A COLOR STABILIZING AND PRESERVING SOLUTION CONTAINING ESSENTIALLY A VOLATILE WATER-DISSOLVING MONOHYDRIC ALCOHOL AND THIOUREA, SAID SOLUTION BEING ADJUSTED TO A PH CORRESPONDING SUBSTANTIALLY TO THE PH OF THE LIQUID MEDIUM OF THE TISSUES IN WHICH THE NATURAL COLORING MATTER IS SUSPENDED, REMOVING THE TISSUES FROM THE SOLUTION AND PERMITTING THE VOLATILE CONSTITUENTS RETAINED IN THEM TO EVAPORATE, WHEREBY THE NATURAL COLORS OF THE TISSUES ARE STABILIZED AND THEIR PHYSICAL SHAPES ARE RETAINED, THEN IMPREGNATING THE TISSUES WITH A MEMBER SELECTED FROM THE GROUP CONSISTING OF POLYETHYLENE GLYCOL, GLYCEROL BORATE, SORBITOL BORIPHOSPHATE, SORBITOL BORATE, SORBITOL CITRATE, SUCROSE AND HEXOSE AND THEN APPLYING TO SAID TISSUES A SUBSTANTIALLY TRANSPARENT MOISTURE-RESISTANT RESINOUS COATING. 